2D MOFs and Zeolites for Composite Membrane and Gas Separation Applications: A Brief Review

Abstract

Commercial membranes have predominantly been fabricated from polymers due to their economic viability and processability. This choice offers significant advantages in energy efficiency, cost-effectiveness, and operational simplicity compared to conventional separation techniques like distillation. However, polymeric membranes inherently exhibit a trade-off between their permeability and selectivity, which is summarized in the Robeson upper bound. To potentially surpass these limitations, mixed-matrix membranes (MMMs) can be an alternative solution, which can be constructed by combining polymers with inorganic additives such as metal−organic frameworks (MOFs) and zeolites. Incorporating high-aspect-ratio fillers like MOF nanosheets and zeolite nanosheets is of significant importance. This incorporation not only enhances the efficiency of separation processes but also reinforces the mechanical robustness of the membranes. We outline synthesis techniques for producing two-dimensional (2D) crystals (including nanocrystals with high aspect ratio) and provide examples of their integration into membranes to customize separation performances. Moreover, we propose a potential trajectory for research in the area of high-aspect-ratio materials-based MMMs, supported by a mathematical-model-based performance prediction.

Mixed Matrix Membranes Based on MFI Zeolite Nanosheets with Tunable Thickness for CO2/CH4 and H2/CH4 Separation

“…Compared to 1D nanofibers and 3D nanoparticles, adding 2D nanosheets into polymeric matrixes has been proved to be more effective as much less additives but enhancing the gas separation performance significantly . Similar to other representative 2D materials, e.g., graphene, GO and MXene, great efforts have also been dedicated to developing 2D zeolites in recent years . Both top-down exfoliation and bottom-up synthesis methods have been developed for 2D zeolite .…”

“…Applying zeolites, such as Si-CHA, SAPO-34, and SSZ-13, as nanofillers in MMMs for CH 4 purification has also been reported over a long time . Specifically, MFI-like zeolites, which have sinusoidal pores in the a -axis and c -axis, as well as one-dimensional straight pores in the b -axis, is favorable for gas diffusion. , Coupled with their large surface area, MFI zeolites have been considered as promising nanofillers in MMMs. − A molecular simulation and Monte Carlo study demonstrated that adding MFI nanofillers into polymeric matrixes can greatly improve their CO 2 /CH 4 separation performance …”